Field of Invention
The present invention relates to a technical field of membrane, and more particularly to a method for preparing a homogeneous braid-reinforced (HMR) PPTA hollow fiber membrane.
Description of Related Arts
Poly(p-phenylene terephthamide) (PPTA) has excellent physical and chemical stability, high temperature resistance, alkali resistance, fungus resistance, organic solvent resistance, high strength and modulus. The tensile strength is next to inorganic fiber. PPTA is an important raw material for producing high performance aromatic polyamide fiber, and it is also an ideal material for producing high performance separation membrane. However, PPTA is generally only dissolved few inorganic acid solutions such as concentrated sulfuric acid because of “non-soluble and non-melting”. Further, it has poor strength that PPTA hollow fiber membrane is fabricated by solution phase inversion method. Therefore, in the membrane separation process, the homogeneous hollow fiber membranes which subject to high pressure water flow pulsation or disturbance for a long time are easily fractured and damaged by the high-pressure hydraulic backwashing process or pollutants deposition, which will affect the quality of filtrate.
Polymer membrane materials (such as membrane bioreactor (MBR)) are widely used in seawater desalination, food processing, pharmaceutical, and other water treatment fields. However, as for the separation and purification in petrochemical, printing and dyeing, organic solvents and other special areas, the membrane material faces a severe situation due to high mechanical strength of the membrane material is needed.
Reinforced hollow fiber membrane is becoming a highlight of research. In general, there are two methods for preparing reinforced hollow fiber membranes:
One is a porous membrane matrix reinforced hollow fiber membrane. Chinese patent CN102600733A discloses a reinforced polyvinyl fluoride hollow fiber membrane and a preparation method thereof, which prepares a hollow fiber membrane with excellent strength by melting spinning, then the PVDF surface separation layer is evenly coated on the porous membrane matrix. According to polymer components of the surface separation layer and the porous membrane matrix, the porous membrane matrix reinforced hollow fiber membrane is classified into homogeneous reinforced hollow fiber membrane and heterogeneous reinforced hollow fiber membrane. Chinese patent CN103100307A discloses the characteristic of phase interfacial bonding of reinforced hollow fiber membranes, which demonstrates that the characteristic of phase interfacial bonding of the homogeneous reinforced hollow fiber membrane is significantly better than that of the heterogeneous reinforced hollow fiber membrane.
The other one is a fiber-reinforced hollow fiber membrane which comprises filament yarn-reinforced hollow fiber membrane and hollow tubular braid-reinforced membrane. For the filament yarn-reinforced hollow fiber membrane, several filament yarns and casting solution are extruded from a newly redesigned hollow fiber spinneret at the same time, so that the filament yarns are embedded in the polymer membrane in the process of composite membrane. For the braid-reinforced hollow fiber membrane, according to the composite spinning method of fiber skin/core structure, the casting solution is integrated with outer surfaces of hollow tubular braids, then they are prepared into tubular braid-reinforced membrane by non-solvent induced phase inversion method. Methods for preparing fiber-reinforced hollow fiber membranes are disclosed in patents such as U.S. Pat. No. 5,403,485A, CN1864828, CN103432916A, CN1695777 and CN102389721A.
Conventional separation layer material of reinforced hollow fiber membranes comprises polyacrylonitrile (PAN), polyvinyl fluoride (PVDF) and polyvinyl chloride (PVC). Because they are poor chemical stability, the conventional reinforced hollow fiber membranes are easy to swell and even dissolve under harsh environments such as high temperature and organic solvents, which seriously restricts the operation life of the membrane materials. At present, inorganic membranes or cross-linked polymer membranes are applied in these harsh environments. However, inorganic membranes are expensive and preparation process is complex. Moreover, the cross-linked polymer membranes are usually hydrophobic materials, or the hydrophilic materials added into membrane irreversibly decrease in the separation process, resulting in poor anti-fouling and anti-bacteria, which also seriously shortens operation life and increases costs. The applicant has previously applied a method for preparing PPTA porous hollow fiber membrane (Chinese application CN104353372A), but the homogeneous PPTA porous hollow fiber membrane prepared (surface separation layer of composite membrane is made from the same casting solution) is poor mechanical properties in the separation process and is easy to be broken, which is still not able to meet the requirements of actual industrial application.
Within search scope of applicant, the literature about the homogeneous tubular braid-reinforced (HMR) PPTA hollow fiber membrane of the present invention has not been found.